Radial solder ball pattern for attaching semiconductor and micromechanical chips

ABSTRACT

A radial solder ball pattern is described for a printed circuit board and for a chip to be attached to the printed circuit board is described. In one example, the pattern comprises a central power connector area having a plurality of power connectors to provide power to an attached chip, a signal area having a plurality of signal connectors to communicate signals to the attached chip, an edge area surrounding the signal area and the central power connector area, and a plurality of traces each coupled to a signal connector, the traces extending from the respective coupled signal connector away from the central power connector to connect to an external component, wherein the signal connectors are placed in rows, the rows having a greater separation near the edge area than near the central area.

FIELD

The present description is related to solder ball patterns for attachingchips to socket and system boards and, in particular, to a radialpattern.

BACKGROUND

Computing systems use a printed circuit board which is referred to as asystem board, logic board, or motherboard to connect all of thecomponents of the system together. The board can include connectors forexternal components, such as power supplies, mass memory and userinterface devices, slots for memory and add-on cards, and holes toconnect pins of chips and discrete components such as capacitors, andresistors. These parts of the board are adapted to suit the particularcomputing system. The chips to be attached will also vary with differentcomputing systems. In some cases, chips are soldered directly to theboard and, in other cases, a socket is soldered to the board and then achip is clamped into the socket. This makes it easier to replace thechip. The board provides a solid structure for attaching parts and alsouses copper traces to electrically connect parts and connectors to eachother.

In chip manufacture, the chips are being made smaller and more complex.In general, this reduces cost and improves performance. The reduced sizeresults in less surface area for external connections and the increasedcomplexity results in more external connections that will be made. Theconnections are made by solder balls or pins on the exterior surface ofthe chip. At the same time, the printed circuit board imposes atechnical limitation on the density of the connections to the chip.There is a limit to how near two connections on a printed circuit boardmay be and still be physically and electrically separate from eachother. This limit depends on how the printed circuit board is made. Aless expensive printed circuit board will require more distance betweennearby connections. In most cases, the chip is able to support muchhigher connection density than the printed circuit board.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are illustrated by way of example, and not by way oflimitation, in the figures of the accompanying drawings in which likereference numerals refer to similar elements.

FIG. 1 is a side view diagram of a package attached to a printed circuitboard according to an embodiment.

FIG. 2 is a side view diagram of a package attached to a socket that isattached to a printed circuit board according to an embodiment.

FIG. 3 is a diagram of a top plan view of a portion of a system boardthat includes lands or pads for attaching a chip or a chip socketaccording to an embodiment.

FIG. 4 is a bottom view diagram of a portion of the system board with anattachment area with a radial star via pattern according to anembodiment.

FIG. 5 is a bottom view diagram of the attachment area of FIG. 4according to an embodiment.

FIG. 6 is a bottom view diagram of the attachment area of FIG. 4indicating how the radial star pattern may be defined according to anembodiment.

FIG. 7 is a diagram of a top view of a chip attachment area in whichthree of four quadrants have a radial star ball pattern according to anembodiment.

FIG. 8 is a diagram of a top view of a chip attachment area in which twoof four quadrants have a radial star ball pattern according to anembodiment.

FIG. 9 is a diagram of a top view of a chip attachment area in which oneof four quadrants has a radial star ball pattern according to anembodiment.

FIG. 10 is a block diagram of a computing device suitable for use withembodiments.

DETAILED DESCRIPTION

As described herein, more connections may be made on a printed circuitboard in the same space. This is presented herein as more routable I/Oon a board, such as a type 3 4 layer (4L) motherboard without increasingthe package form factor. The improvements are obtained by rearrangingthe package ball pattern in the middle span region to optimize thedifferential pair routing. This increases the routable I/O count on themotherboard.

FIG. 1 is a side view diagram of a portion of a computing system. Inthis example a chip 102 is soldered 106 directly to a motherboard 104.The chip is shown as having a heat sink 108 on its back side and asolder ball array 106 on its front side attached to the motherboard. Insurface mount technology (SMT), the chip and the motherboard both havematching arrays of lands. Solder balls are attached to the lands on thechip and the chip is placed on the motherboard. Both are heated, forexample in a reflow furnace, to melt the solder and attach the chip tothe board.

FIG. 2 is a side view diagram of a portion of an alternative computingsystem. In this example, the chip 102 is attached to a socket 112 by aclamp 118. The clamp is part of or attached to the socket. The socket issoldered 116 to the motherboard 114. The chip 102, including its heatsink 108, is clamped to the socket and held in place until the clamp isreleased.

The described embodiments may be applied to any of variety of differentchips and is particularly well suited to chips with a high I/O count,such as central and graphics processors, signal processors, radios, andhigh density communications interfaces. The approach is also suitablefor chips with a low I/O count and allows the I/O to be confined to asmaller area then otherwise might be possible. “Chip,” as used hereinrefers, generally to one or more dies attached to a substrate, orpackage substrate. The dies may also be covered with a heat spreader, aplastic cover, a molded resin, or other protector. The dies may bestacked, placed side-by-side or embedded together in some way. The chipmay also have passive components, antennas, and other componentsincluding additional connectors on the sides or top.

A conventional ball pattern for a printed circuit board is a grid. Afully gridded ball pattern has a regular array of rows and columns wherethe distance between each row and between each column is at least aslarge as the technical limit of the circuit board. A further constrainis that each of the balls in the pattern must be connected somewhere. A4L board, for example has four wiring layers including the top layer. Ifa central ball is coupled to a component other than the chip, then theremust be room for a copper trace to extend from that central ball tobeyond the area of the chip without overlapping with another trace onthe same layer.

FIG. 3 is a diagram of a top plan view of a portion of a system boardthat includes lands or pads for attaching a chip or a chip socket. Theparticular attachment structure and technology may be adapted to suitany particular chip. Each land 141 is attached to a trace 142 whichconnects to a via 143 that connects that land to a trace on one of threecopper wiring layers below the illustrated top surface. Alternatively,as shown in other figures, a land may attach to a trace that leads awayfrom the attachment area on the top surface. The traces and vias requirea minimum separation from each other trace and via. The minimum separateis determined by the structure and material of the board.

In some embodiments, the L4 board provides power on layer 2 (L2) andlayer 3 (L3). The signaling traces are on layer 1 (L1) the top layer andlayer 4 (L4) the lowest copper layer. However, the layers may be inother layers and there may be more or fewer layers to suit differentcomputing devices. In the FIG. 3 example, a signaling trace may beeither on the surface of L1 or connected from a pad through a via to L4.The L4 traces then connect through vias to reach other components.

The attachment area 122 has lands, pads, or balls in a pattern that hasmultiple areas. At the center is a middle span region 124. A packageedge area 126 surrounds all of the other connectors. An outside area 128is not part of the attachment area but is outside the area of the chipand has surface traces to connect the attachment points to othercomponent and connectors (not shown). There may also be other traces(not shown) in copper layers below the illustrated top surface.

Between the middle span region 124 and the edge 128 is the primary spanregion 126, this is divided in this example into four primary spanquadrants 132, 134, 136, 138. These quadrants have a novel radial starball pattern which optimizes the balls and the vias through the board.For a 4L type 3 motherboard, the vias provide another space limitationto the I/O density. With this ball pattern, more I/O is able to berouted out from the primary span region compared to the rectangular gridpattern. Each quadrant may be seen as being split by a diagonalreference line 131, 133, 135, 137. This line may be used to determineball positions, but is not a part of the structure nor are thehorizontal and vertical lines that are used to define the fourquadrants.

FIG. 4 is a bottom view diagram of a portion of the system board with anattachment area with a radial star via pattern. This view shows the L4traces from contact vias that extend to the top surface shown in FIG. 3.The signal vias 143 of the top layer end at the vias shown here. The L4layer is at the bottom and would be visible through a transparentdielectric bottom coating or if the bottom dielectric were not yetapplied. The board 202 has middle span region 204 (shown for referencebut not actually visible at L4), a primary span quadrant 206 on one sideof the middle span region and an edge area 208 bounding the quadrant.The middle span region is shown as a simple grid pattern for simplicity.The edge area has traces 212 extending away from the quadrant to othercomponents.

In the primary span quadrant 206, the signal connector vias arerearranged to give space for the better routing scheme described herein.The lands or solder balls of FIG. 1 are similarly rearranged. Thisbetter routing scheme may be used to reduce the cost of a chip packageby allowing for more I/O pads on the same or a smaller chip. The landsmay be considered as being in lines that approximate rows and columnsbut curve from a central location near the middle span region 204 out tothe edge region 208. The lines curve radially outward from the center toform a star ball pattern. Viewed another way, the lines each show aregular or irregular divergence from the line that is placed before it.

Considering one of these lines 220, it has ground vias 222 as well assignal vias 224, 230. The ground vias may connect a land on the chipdirectly to power or ground without any connecting trace on this layer.The signal vias that are routed on this layer either connect to a viathrough a trace or connect to a longer breakout trace 226 that carriesthe signal from the land through a breakout space 228 indicated by thearrow past the edge area 208.

The breakout space is large enough to allow all of the breakout tracesto pass through to the edge area. As shown with one of the lines of vias220, the line is not strictly horizontal but curves downward away fromthe line above it to enlarge the breakout space 228. If the line 220were horizontal, then there would be room for at most four traces in thebreakout space. However the fourth via 230 from the center along theline is lower than the previous via or, in other words, it is spacedfarther from the line directly above. This makes room for another traceto extend from the fourth via without interfering with the five tracesthat are already running to the edge area. The next via is moved stilllower or farther from the line above to make room for yet another trace.Since all of the remaining vias in the line also have traces on L1extending to the edge, each succeeding via is lower than the one on themiddle side of the line. The line of vias 220 curves downward away fromthe line of vias above it so far that the breakout area 228 has room foreight traces instead of the four that otherwise might be accommodated.

Using this approach, after the first line or row, the next row divergesfrom the first row by an amount determined by the number of traces thatare to be accommodated. When each via has a trace, then the row extendsalong a straight diagonal away from the row before it. When there is aground via then the diagonal stops and the row extends along the rowbefore it until another trace is added.

In this example, the width of each breakout area 228 is indicated byarrows. As shown there are narrower and wider breakout areas. Any I/Othat is routed to another component through the board passes through thebreakout area. Accordingly an increase in the total width of thebreakout areas allows for more I/O routing. In a rectangular grid, thebreakout areas are all the same size, however, in this example many ofthe breakout areas are larger than others. Dotted lines are used to showthe area allocated to traces from near the center toward the edge of theattachment area near the breakout area. As shown, these trace areas arenarrower in the center and then expand or widen as the sides approachthe outer edge of the middle span regions. This increase in the width ofthe dotted line trace areas shows how the room available for traces isimproved over a rectangular grid.

FIG. 5 is a bottom view diagram of the attachment area of FIG. 4. Inthis diagram instead of highlighting the break out areas as in FIG. 4,differential pairs are highlighted using small boxes around each pairand labeled from 1 to 32. Much of the data for many chips is carriedwith differential signaling. For efficiency in the routing inside thechip, the two signal lines of a differential pair are next to eachother. Referring to the row of vias at the top left of the diagram, theleftmost one 236 is a ground, the next two 234 to the right in box 32are a differential pair, the next one 238 to the right is a ground, thenext two pairs 240, 242 to the right in boxes 30, 31 are two moredifferential pairs and the left most ball 244 is a ground. This is anexample of how the vias may be connected and how different rows may havedifferent sequences of connections as shown. The order of connectionsbetween ground vias and differential pairs may be changed in eachexample to suit different implementations and different chip structures.

In this example, the middle span region is entirely or almost entirelypower vias. These power vias are balanced by ground vias that aredistributed through the quadrants. The power and ground vias are coupledto L2 and L3 as mentioned above and they may all be connected to eachother so that individual traces are not required for each power via andfor each ground via.

While it is useful and necessary to have ground vias, in a rectangulargrid, the ground vias are used whenever there is not enough room for atrace to an external connection. The differential signal connectionseach require two traces that lead outward to make an externalconnection. When there is no room for two traces to extend past the edgearea, then a ground via may be inserted. When there are too many groundvias, then the balls of the grid are wasted.

The reason for too many ground vias is that many balls are not able toconnect to routing in 4L of the motherboard because of the narrowrouting space. The radial star pattern has removed these wasted groundvias by increasing the breakout areas and adding more traces. Byexchanging the gridded I/O ball pattern for the radial star ball patternthere is more I/O breakout area so that the diagonal wasted area ingridded ball pattern may be fully utilized. The limitations of viaplacement and signal breakout can be overcome by rearranging the griddedball-to-ball pattern to create more room for signal breakout.

FIG. 6 is a bottom view diagram of the attachment area of FIG. 4indicating how the radial star pattern may be defined. The placement ofthe balls in the pattern is subject to several restrictions. The printedcircuit board structure and manufacturing technology require a minimumspacing between any two balls and also a minimum spacing between any twotraces. This limit is determined in part by the structure of the board,the level of insulation provided by the board between two structures,the accuracy in placing holes and traces, the expected voltage andcurrent of the signals, etc.

The specific shape and form of the rows in the radial star ball patternmay be determined in a variety of different ways. In the illustratedexample, the placing of the rows may begin along the edge of thequadrant with a first row labeled as “1.” Any other straight line of thequadrant may be used or a straight line may be established anywhere inthe quadrant as a starting place. This first row is placed with anappropriate number of signal connectors. The number of connectors may bedetermined by the distance from the edge 208 to the central power area204. Each power connector requires a certain distance from the nextclosest power connector. This minimum distance may be used to place thesignal connectors along the row. In the illustrated example, there isroom for 8 signal connectors.

The number of signal connectors may be determined by applying the sizeof each via connector (Csize) and the required spacing (Cspace) to thetotal available distance (Dt). This may be expressed in an equation thatcan be solved for n, the maximum allowable number of vias. In theillustrated example, n=8 for row 1.

nCsize+(n−1)Cspace=Dt  (Eq. 1)

Having established and set a starting row of vias aligned straight withthe quadrant edge, the signal breakout may be determined. As with thevias there is a minimum spacing necessary for the traces. This spacingis function of the substrate layer technology and the anticipated signalvoltage and current. The space required for a trace is the width of thetrace plus the minimum spacing between traces. In practice, with thefirst row set, then the vias will be assigned and the traces routed.

As explained above, for differential signaling adjacent vias may beassigned to opposing sides of a differential pair. In addition some viasare assigned to be ground vias. The ground vias are best distributedthrough the row. In the first example of 8 vias, there are threedifferential pairs and two ground vias. The particular position of eachground via may be adapted to suit different implementations. The tracesare then routed. In this case, vias for two pairs are routed on the leftside of the row closest to the quadrant edge and one pair is routed onthe right side of the row.

Adding up the trace spacing then determines the position for the nearestvias of the next rows. This relationship may also be expressed as aformula in which the trace size or width (Tsize) plus the minimumspacing between traces (Tspace) is combined with the minimum spacebetween a trace and via (TVspace) for the via at either end.

nTsize+(n−1)Tspace+2TVspace=Via to Via Spacing  (Eq. 2)

In this example the next row 2 may be started for simplicity at astandard distance which, in this case, is sufficient for four traces.The top via is placed at that distance from the top via of the next row.It has a breakout trace alongside the two breakout traces of the firstrow, row 1. The second via may be placed at the same distance from thesecond via of row 1. The second via also has a breakout trace. Thismakes for 4 traces, the maximum number allowed by the spacing indicatedas E. The third via is a ground that has no trace. The fourth via is asignal via and has a breakout trace. Because the traces are smaller thanthe vias, the fourth via's trace may be directed along the other fourtraces without moving the via. From vias one to four the row is astraight line. The fifth and next via must allow room for 5 tracesbecause of the trace from the fourth via. As a result the spacingbetween row 1 and row 2 is increased at the fifth via. This spacing isindicated as D.

The next two vias are also signal vias and add two more traces to thetotal number of traces to be accommodated in the same breakout area.With each additional via, spacing between the rows is further increasedby moving the next via of row 2 farther from row 1 than the via aboveit. The spacing for the sixth via, indicated as C accommodates 6 traces.The next via is still farther from row 1 at a distance B for 7 tracesand the last via is at distance A for 8 traces. This increasing distancecreates an angular diversion from the direction of row 1.

This process continues with mapping each row until hitting the 45 degreediagonal quadrant line 235. The area is configured from a quadrantdivider 250 to the diagonal quadrant line 235. However, the area may beconfigured in another order. While the diagonal is shown as being a 45degree line, the diagonal quadrant line may be at any other angle, suchas 30, 60, or some other number of degrees. Any other way of dividingthe main span area 126 may be used instead of straight and diagonallines. In addition, the rows may be mapped in the opposite orderstarting at the diagonal and progressing back to the rectangular line.For the next row, row 3, the first via is placed at this same distance.The first two vias are differential signal vias and the traces extendfrom the vias to the breakout area at the edge area 208. However,because of the shift of the vias in row 2, the breakout traces do notproceed in a straight line to the edge but veer to the right to avoidthe shifted vias of row 2.

As shown in row 3, the fifth via from the top is shifted left to keep aspacing J for 3 traces. This is caused by the fifth via in row 2 beingshifted to keep a spacing for 5 traces. Since the vias of row 2 eachshift to accommodate one more trace, the vias of row 3 each shift toaccommodate 2 traces, the added trace of row 2 and an added trace fromrow 3. Specifically via 6 is shifted to create a spacing H for 4 traces.Via 7 is shifted to create a spacing G for 5 traces. Via 8 is shifted tocreate a spacing F for 8 traces. The 8 traces include one from row 3 andtwo from row 4. This creates a curve in row 3 away from row 2.

Row 4 shows an additional constraint. In this example, the diagonalquadrant edge is used as a boundary for placing the vias. The diagonalquadrant line 235 then limits the placing of the top via of row 4. Thetop via of row 4 is placed below the diagonal quadrant line and with the4 trace spacing from row 3 as was used with first three rows. The samespacing principles are then used to plot the vias of row 4. Due to thelower start caused by the quadrant, there is room for only 5 vias inthis row. The last via however, is not used to leave space for breakouttraces. The next row has 5 vias and the last row also has five vias. Thetraces however are allowed to extend through rows in order to reduce thelength and total space used.

After the lower half of the quadrant rows are plotted, then thepopulation is restarted from the opposite quadrant edge with row 6. Thisrow at the opposite quadrant edge again follows the edge and isstraight. It is the same as row 1 except that the positions of theground vias and signal vias are changed. Rows 7 and 8 are also the sameas rows 1 and 2, respectively except for the placement of the groundvias. This is not necessary but is likely if the same rules are followedfor placing the first via of the row and for spacing.

Row 9 is different from row 3 or 4 because it is using a different rule.The same is true for rows 10 and 11. For these rows, the diagonalquadrant edge is violated. Because the first set of rows did not use allof the available space in the first part of the quadrant. These rowsplace the first via across the quadrant line to use the space thatotherwise is not occupied. The same spacing rules apply.

There is one further constraint shown in this example, and that is thatthe ground vias are placed in straight lines perpendicular to the rows.This simplifies the routing of the ground layers at L2 or L3. Theplacement of the ground vias affects the traces at L4 because the groundvias do not have traces at L4.

The use of an interconnect area can be characterized by considering thenumber of differential signal vias in a particular area. The quadrantshown in FIG. 6 has 64 signal vias to support 32 differential pairs. Thestandard gridded pattern supports only 26 pairs because signal tracescannot reach all of the possible via locations of the grid. As mentionedabove, these via locations with no trace are used for ground vias. Thedescribed pattern has better Second Level Interconnect (SLI) density byover 7%. For all four quadrants there are 24 more signal pairs supportedin the same package form factor. Looked at another way, to support thesame number of signal pairs with a gridded or with any of many othertypes of patterns, a larger package would be required. A larger packagewith a larger I/O area is more expensive and may also necessitate alarger product form factor.

In the diagram of FIG. 3, all four quadrants 132, 134, 135, 136 use theradial star pattern, however, this is not necessary. FIG. 7 is a diagramof a top view of a chip attachment area 302 similar to that of FIG. 3 inwhich one of the four quadrants 304 has a rectangular grid pattern. Theother three quadrants use the radial star pattern.

Similarly in FIG. 8 a chip attachment area 312 has two quadrants 314,316 with a gridded pattern. While these quadrants are shown as beingadjacent they may opposite each other so that a radial star pattern isbetween them.

In FIG. 9, a chip attachment area 322 has three gridded patternquadrants 324, 326, 328. The particular positioning of the gridded arearelative to the radial star area may be adapted to suit differentimplementations. In addition while a gridded pattern is shown withstraight, even, orthogonal rows and columns, other types of patterns maybe mixed with the radial star pattern. The description herein ispresented in the context of quadrants. This is a common way of layingout connections in a chip attachment area. However, the area may bedivided into halves, thirds, fifths, etc. The areas may be another shapeother than square. The square blocks with diagonals is suitable for manyapplications but other shapes and dividers at other angles may be usedto lay out the radial star ball pattern.

While the chip attachment area has been presented in the figures asbeing a portion of a motherboard or socket, the chip will have amatching pattern so that the lands or pads of the motherboard are ableto connect to the lands or pads of the chip. Any of the L1 diagrampatterns, such as those of FIGS. 3, 7, 8, and 9 also show the patternthat will be formed on the chip in order to connect to the pattern onthe board or socket. The chip substrate is typically made of a higherquality material than the motherboard, in which case the spacinglimitations of the motherboard will still determine the minimum spacingbetween vias and traces as described above.

FIG. 10 illustrates a computing device 100 in accordance with anembodiment. The computing device 100 houses a board 2. The board 2 mayinclude a number of components, including but not limited to a processor4 and at least one communication chip 6. The processor 4 is physicallyand electrically coupled to the board 2. In some implementations the atleast one communication chip 6 is also physically and electricallycoupled to the board 2. In further implementations, the communicationchip 6 is part of the processor 4.

Depending on its applications, computing device 100 may include othercomponents that may or may not be physically and electrically coupled tothe board 2. These other components include, but are not limited to,volatile memory (e.g., DRAM) 8, non-volatile memory (e.g., ROM) 9, flashmemory (not shown), a graphics processor 12, a digital signal processor(not shown), a crypto processor (not shown), a chipset 14, an antenna16, a display 18 such as a touchscreen display, a touchscreen controller20, a battery 22, an audio codec (not shown), a video codec (not shown),a power amplifier 24, a global positioning system (GPS) device 26, acompass 28, an accelerometer (not shown), a gyroscope (not shown), aspeaker 30, a camera 32, and a mass storage device (such as hard diskdrive) 10, compact disk (CD) (not shown), digital versatile disk (DVD)(not shown), and so forth). These components may be connected to thesystem board 2, mounted to the system board, or combined with any of theother components.

The communication chip 6 enables wireless and/or wired communicationsfor the transfer of data to and from the computing device 100. The term“wireless” and its derivatives may be used to describe circuits,devices, systems, methods, techniques, communications channels, etc.,that may communicate data through the use of modulated electromagneticradiation through a non-solid medium. The term does not imply that theassociated devices do not contain any wires, although in someembodiments they might not. The communication chip 6 may implement anyof a number of wireless or wired standards or protocols, including butnot limited to Wi-Fi (IEEE 802.11 family), WiMAX (IEEE 802.16 family),IEEE 802.20, long term evolution (LTE), Ev-DO, HSPA+, HSDPA+, HSUPA+,EDGE, GSM, GPRS, CDMA, TDMA, DECT, Bluetooth, Ethernet derivativesthereof, as well as any other wireless and wired protocols that aredesignated as 3G, 4G, 5G, and beyond. The computing device 100 mayinclude a plurality of communication chips 6. For instance, a firstcommunication chip 6 may be dedicated to shorter range wirelesscommunications such as Wi-Fi and Bluetooth and a second communicationchip 6 may be dedicated to longer range wireless communications such asGPS, EDGE, GPRS, CDMA, WiMAX, LTE, Ev-DO, and others.

The processor 4 of the computing device 100 includes an integratedcircuit die packaged within the processor 4. In some implementations,the packages that include the processor, memory devices, communicationdevices, or other components may have a radial star ball pattern tomatch a similar radial star ball pattern of a chip attachment area ofthe board. The term “processor” may refer to any device or portion of adevice that processes electronic data from registers and/or memory totransform that electronic data into other electronic data that may bestored in registers and/or memory.

In various implementations, the computing device 100 may be a laptop, anetbook, a notebook, an ultrabook, a smartphone, a tablet, a personaldigital assistant (PDA), an ultra mobile PC, a mobile phone, a desktopcomputer, a server, a printer, a scanner, a monitor, a set-top box, anentertainment control unit, a digital camera, a portable music player,or a digital video recorder. In further implementations, the computingdevice 100 may be any other electronic device that processes data.

Embodiments may be adapted to be used with a variety of different typesof packages for different implementations. References to “oneembodiment”, “an embodiment”, “example embodiment”, “variousembodiments”, etc., indicate that the embodiment(s) so described mayinclude particular features, structures, or characteristics, but notevery embodiment necessarily includes the particular features,structures, or characteristics. Further, some embodiments may have some,all, or none of the features described for other embodiments.

In the following description and claims, the term “coupled” along withits derivatives, may be used. “Coupled” is used to indicate that two ormore elements co-operate or interact with each other, but they may ormay not have intervening physical or electrical components between them.

As used in the claims, unless otherwise specified, the use of theordinal adjectives “first”, “second”, “third”, etc., to describe acommon element, merely indicate that different instances of likeelements are being referred to, and are not intended to imply that theelements so described must be in a given sequence, either temporally,spatially, in ranking, or in any other manner.

The drawings and the forgoing description give examples of embodiments.Those skilled in the art will appreciate that one or more of thedescribed elements may well be combined into a single functionalelement. Alternatively, certain elements may be split into multiplefunctional elements. Elements from one embodiment may be added toanother embodiment. For example, the specific location of elements asshown and described herein may be changed and are not limited to what isshown. Moreover, the actions of any flow diagram need not be implementedin the order shown; nor do all of the acts necessarily need to beperformed. Also, those acts that are not dependent on other acts may beperformed in parallel with the other acts. The scope of embodiments isby no means limited by these specific examples. Numerous variations,whether explicitly given in the specification or not, such asdifferences in structure, dimension, and use of material, are possible.The scope of embodiments is at least as broad as given by the followingclaims.

The following examples pertain to further embodiments. The variousfeatures of the different embodiments may be variously combined withsome features included and others excluded to suit a variety ofdifferent applications. Some embodiments pertain to a printed circuitboard that includes a central power connector area having a plurality ofpower connectors to provide power to an attached chip, a signal areahaving a plurality of signal connectors to communicate signals to theattached chip, an edge area surrounding the signal area and the centralpower connector area, and a plurality of traces each coupled to a signalconnector, the traces extending from the respective coupled signalconnector away from the central power connector to connect to anexternal component, wherein the signal connectors are placed in rows,the rows having a greater separation near the edge area than near thecentral area.

In further embodiments the separation of the rows near the edge area isgreater than a number of traces between adjacent rows multiplied by awidth of each trace and a minimum trace spacing.

In further embodiments the rows diverge away from a first row withdistance from the central area.

In further embodiments at least some of the rows diverge from the firstrow along a straight diagonal.

In further embodiments a second row has connectors that are shifted awayfrom an adjacent first row to accommodate a trace between the first rowand the second row.

In further embodiments the first row is straight and the second rowcurves away from the first row.

In further embodiments the curved rows include power connectors withouttraces to provide power to the attached chip.

In further embodiments the traces are formed on a layer of the boardbelow the signal connectors.

In further embodiments the power connectors include vias through theboard to a layer of the board below the power connectors

In further embodiments the signal connectors comprise lands.

In further embodiments the signal connectors comprise solder balls.

Further embodiments include the attached chip having a plurality ofconnection lands aligned to connect to the power connectors and thesignal connectors.

Some embodiment pertain to a method that includes laying out a first rowof signal connectors to communicate signals to an attached chip in asignal area of a printed circuit board between a central power connectorarea, having a plurality of power connectors to provide power to anattached chip, and an edge area surrounding the signal area and thecentral power connector area, the first row extending along a straightline in the signal area from the central power connector area to theedge area, laying out a plurality of traces, each coupled to a signalconnector of the first row, the traces extending from the respectivecoupled signal connector away from the central power connector toconnect to an external component, and laying out a second row of signalconnectors, the second row having a greater separation from the firstrow near the edge area than near the central area.

In further embodiments laying out a second row comprises laying out aseparation of the second row that is greater near the edge area than anumber of traces between the first row and the second row multiplied bya width of each trace and a minimum trace spacing.

In further embodiments the second row has connectors that are shiftedaway from the first row to accommodate a trace between the first row andthe second row.

In further embodiments the signal area is rectangular having four sides,each side having a quadrant line extending from the center of theattachment area to a middle of a respective side, and wherein the firstrow is laid out along a quadrant line and the second row is laid outalong the first row on a side opposite a quadrant line.

In further embodiments each quadrant is divided by a diagonal line fromthe center of the attachment area to a corner of the edge area of therectangular signal area, the method further comprising laying outadditional rows to the diagonal.

Some embodiments pertain to a computing system that includes aprocessor, a memory, and a printed circuit board connected to theprocessor to the memory to couple the processor to the memory, theprinted circuit board having a central power connector area having aplurality of power connectors to provide power to the processor, asignal area having a plurality of signal connectors to communicatesignals to the processor, an edge area surrounding the signal area andthe central power connector area, and a plurality of traces each coupledto a signal connector, the traces extending from the respective coupledsignal connector away from the central power connector to connect to anexternal component, wherein the signal connectors are placed in rows,the rows having a greater separation near the edge area than near thecentral area.

In further embodiments the separation of the rows near the edge area isgreater than a number of traces between adjacent rows multiplied by awidth of each trace and a minimum trace spacing.

In further embodiments a second row has connectors that are shifted awayfrom an adjacent first row to accommodate a trace between the first rowand the second row.

1. A printed circuit board comprising: a central power connector areahaving a plurality of power connectors to provide power to an attachedchip; a signal area having a plurality of signal connectors tocommunicate signals to the attached chip; an edge area surrounding thesignal area and the central power connector area; and a plurality oftraces each coupled to a signal connector, the traces extending from therespective coupled signal connector away from the central powerconnector to connect to an external component, wherein the signalconnectors are placed in rows, the rows having a greater separation nearthe edge area than near the central area.
 2. The board of claim 1,wherein the separation of the rows near the edge area is greater than anumber of traces between adjacent rows multiplied by a width of eachtrace and a minimum trace spacing.
 3. The board of claim 1, wherein therows diverge away from a first row with distance from the central area.4. board of claim 3, wherein at least some of the rows diverge from thefirst row along a straight diagonal.
 5. The board of claim 1, wherein asecond row has connectors that are shifted away from an adjacent firstrow to accommodate a trace between the first row and the second row. 6.The board of claim 5 wherein the first row is straight and the secondrow curves away from the first row.
 7. The board of claim 1, wherein thecurved rows include power connectors without traces to provide power tothe attached chip.
 8. The board of claim 1, wherein the traces areformed on a layer of the board below the signal connectors.
 9. The boardof claim 1, wherein the power connectors include vias through the boardto a layer of the board below the power connectors.
 10. The board ofclaim 1, wherein the signal connectors comprise lands.
 11. The board ofclaim 1, wherein the signal connectors comprise solder balls.
 12. Theboard of claim 1, further comprising the attached chip having aplurality of connection lands aligned to connect to the power connectorsand the signal connectors.
 13. A method comprising: laying out a firstrow of signal connectors to communicate signals to an attached chip in asignal area of a printed circuit board between a central power connectorarea, having a plurality of power connectors to provide power to anattached chip, and an edge area surrounding the signal area and thecentral power connector area, the first row extending along a straightline in the signal area from the central power connector area to theedge area; laying out a plurality of traces, each coupled to a signalconnector of the first row, the traces extending from the respectivecoupled signal connector away from the central power connector toconnect to an external component; and out a second row of signalconnectors, the second row having a greater separation from the firstrow near the edge area than near the central area.
 14. The method ofclaim 13, wherein laying out a second row comprises laying out aseparation of the second row that is greater near the edge area than anumber of traces between the first row and the second row multiplied bya width of each trace and a minimum trace spacing.
 15. The method ofclaim 13, wherein the second row has connectors that are shifted awayfrom the first row to accommodate a trace between the first row and thesecond row.
 16. The method of claim 13, wherein the signal area isrectangular having four sides, each side having a quadrant lineextending from the center of the attachment area to a middle of arespective side, and wherein the first row is laid out along a quadrantline and the second row is laid out along the first row on a sideopposite a quadrant line.
 17. method of claim 16, wherein each quadrantis divided by a diagonal line from the center of the attachment area toa corner of the edge area of the rectangular signal area, the methodfurther comprising laying out additional rows to the diagonal.
 18. Acomputing system comprising: a processor; a memory; and a printedcircuit board connected to the processor to the memory to couple theprocessor to the memory, the printed circuit board having a centralpower connector area having a plurality of power connectors to providepower to the processor, a signal area having a plurality of signalconnectors to communicate signals to the processor, an edge areasurrounding the signal area and the central power connector area, and aplurality of traces each coupled to a signal connector, the tracesextending from the respective coupled signal connector away from thecentral power connector to connect to an external component, wherein thesignal connectors are placed in rows, the rows having a greaterseparation near the edge area than near the central area.
 19. The systemof claim 18, wherein the separation of the rows near the edge area isgreater than a number of traces between adjacent rows multiplied by awidth of each trace and a minimum trace spacing.
 20. The system of claim18, wherein a second row has connectors that are shifted away from anadjacent first row to accommodate a trace between the first row and thesecond row.